Gaspar Noé likes to describe himself as "a straight kind of guy and a bit of a wimp". When he was a teenager, he was too squeamish to sit through Sam Peckinpah's Staw Dogs: "I thought it was too heavy to handle. During the rape scene, I had to walk out," he confides in his softly-spoken voice. Discussing a favourite book, JW Dunne's An Experiment with Time - a 1927 study by an English aeronautical engineer who developed his own pet theories about dreams, perception and reality - he sounds like an earnest young philosophy student. None the less, this seemingly placid 38-year-old has now made a movie so extreme that it provoked mass walk-outs and prolonged catcalls - as well as wild applause - during its press screening in Cannes.

Irréversible, which will receive its British premiere at the Edinburgh festival, comes billed as "a violent trip - from hell to paradise". Formally, it is ingenious. Like Martin Amis's Time's Arrow (a book which Noé admits to owning but not to having read), it begins at the end and works forward. Like the Buenos Aires-born director's arresting debut feature, Seul Contre Tous (1998), it is shot in 16mm and blown up to 35mm. Much of the film is improvised. Sequences are held for a small eternity. Sound editing is hyperbolic in the extreme. (When somebody is having his head mashed to a pulp with a fire extinguisher, we hear what sound like thunderclaps.) At times, especially when we're stuck deep in the slimy, dimly lit bowels of the Rectum club (the gay S&M parlour that is the site of much of the film's most explosive violence), it is like being cast back into an expressionist horror movie of the 1920s. ("There is something in the architecture of this movie that is close to Metropolis," Noé acknowledges, a trifle pompously.)

The tone is set right from the outset, as we hear a martial-sounding drum roll over the credits (which, perversely, are projected back to front.) "I liked the drums because it gave me the idea of execution, like when people are being hanged or walking to the scaffold . . . you feel that something tragic is going to happen and that somebody is going to die. Also, it's so elementary. It reminds you of the perception of time - the boom, boom, boom is almost like a watch that you're listening to," says Noé.

Noé himself operated the camera, even at the most chaotic moments. "I was behind, just shaking the camera in every single direction. You get excited also by the violence of the actors. All their energy gives you energy and when they start beating and punching, you do the same thing with your camera. The result may look preconceived but it's totally instinctive."

The central conceit, he argues, isn't so different from that of classical tragedy. The elements are rape and revenge. Once the furies have been unleashed, there is nothing that can be done to stop them. As his director's statement puts it: "Time destroys everything . . . all history is written in sperm and blood . . . premonitions do not alter the course of events."

What so polarised the audiences in Cannes wasn't so much the subject matter or structure as the graphic and prolonged way in which the rape itself was depicted. Three-quarters of an hour into the film, Alex (Monica Bellucci), is attacked and viciously assaulted by a pimp in the subway. There are no cut-aways or rhetorical tricks. What we're presented with is an uninterrupted, nine-minute sequence clearly intended to shock and to disgust.

"Because the subject of the movie was a rape, I said it has to be as powerful as it can be, to be disgusting enough, to be useful," says Noé. "If you do a movie with a rape and don't show it, you hide the point . . . the thing is that if you show it in a disgusting way, you help people to avoid that kind of situation. Like in Clockwork Orange, when they show images of terror to Malcolm McDowell to stop him doing those kind of things, it is useful that it is shown."

The scene was shot six times over two days. Noé says he had no idea how long it was going to last. That was in the hands of Bellucci and the actor playing her assailant. "The results were great the first day but even more perfect on the second . . . they [the actors] were more and more confident with each other and so they could go further and further. I didn't know if it would last for six minutes, 10 minutes, 12 minutes or whatever. The whole scene was in her hands, and even the guy who was playing the rapist was at her service. If she didn't want to do the scene like that, she would have said it. I really admire her for having taken that scene so far."

Bellucci's performance is indeed courageous. She and her husband Vincent Cassel (who plays her boyfriend in the film) are a national obsession in France: a celebrity couple along the lines of Burton and Taylor, or Tom Cruise and Nicole Kidman (hence Noé's remarks about Irréversible being the film Cruise and Kidman should have made with Kubrick instead of Eyes Wide Shut). Noé describes Bellucci (shortly to be seen in the Matrix sequel) as "a mix of Brigitte Bardot and Claudia Cardinale at the same time". She had little obvious to gain by appearing as a rape victim in a lowish budget, arthouse film that - in its detractors' eyes - comes perilously close to exploitation.

Noé is clearly riled by the attacks made on the movie following its Cannes premiere. "People are mad about the movie, but accusing it of misogyny is a stupidity, as is accusing it of homophobia," he complains. "It's not because you have characters that depict aspects of the humankind that you agree with them. I think that Paul Schrader said that about Taxi Driver - just because you give a portrait of a criminal that doesn't mean you are a criminal yourself."

On one level, Irréversible is a companion piece to "bad girl" road movie Baise-Moi, which also featured a brutal rape sequence and the kind of stomach-churning violence that makes Jacobean Revenge drama seem understated. Both films were financed by the same company - Studio Canal offshoot The Wild Bunch. Noé is friendly with the makers of Baise-Moi (the co-director, porn actress Coralie Trinh Thi, appeared in Sodomites, the hardcore safe-sex promo that he made for French TV in the late 1990s). He describes it as "a bomb of energy", and claims that the changes it brought about in French censorship laws enabled him to make Irréversible with complete freedom. When asked about the way distinctions between arthouse and exploitation have begun to blur, he says: "Maybe the audiences are more mature than they used to be."

He is a deceptive film-maker, part polemicist, part aesthete. As critic Tony Rayns once remarked of him: "Scratch a punk and you'll find an art college wannabe inside." Seul Contre Tous superficially resembled one of Fassbinder's morality tales about the little man ground down by the system. Its protagonist, Jean Chevalier (brilliantly played by Philippe Nahon), was a woebegone butcher, just out of jail, without work or money, who vows revenge against the "nigger faggots" and "faggots in suits" responsible for his predicament. Although the film paid lip-service to the conventions of social realism, Noé's interest was less in unemployment, racism and the rise of the right than in making an outrageously skewed psycho-drama about a Travis Bickle-like outsider - and in upsetting as many groups as possible by doing so. "Noé claims to have wanted his film banned . . . to prove its confrontational power," the film magazine Sight and Sound noted at the time. "Instead, a film he had expected to alienate 90% of its audience and draw flak from feminist groups, gay groups, anti-racist campaigners and conservatives has been lavishly praised by the press, communist and conservative alike."

It's a moot point whether he is really saying anything very profound about violence or rape in Irréversible, or whether he's still driven by an adolescent desire to shock. Some of his explanations sound glib. For instance, in describing his two male protagonists, he suggests that the extrovert Marcus (Vincent Cassel's character) is "the guts", while his much quieter friend Pierre (Albert Dupontel) stands for the brain. Disconcertingly, it's Pierre who's behind the most violent act of all. ("The brain takes control of the guts but, at the end, the brain just follows the guts.")

Whatever else, Irréversible is already a succès de scandale . Noé's claims that it is a "feminist" movie sound far-fetched, but he certainly offers an extraordinarily pessimistic view of male sexuality. What's unsettling about the film is not just the bloodletting of the first half, but the way that the characters behave in the moments leading up to it. For instance, Cassel, in the long, seemingly idyllic scene in which he lounges about in bed with Bellucci, uses language that echoes that of the rapist.

It is apt that Irréversible is surfacing in Britain just as Straw Dogs is re-released. The arguments that Peckinpah made in 1971 (namely that he wanted to make audiences "very, very uncomfortable about their potential for violence") are similar to those that Noé advances when I speak to him. Noé, however, argues that he has gone one step further than the old western maestro by making a film that ends - albeit with heavy irony - on an optimistic note.

"Peckinpah was always saying his next movie would be a life-affirming movie. But they never were," Noé notes. "He'd do another revenge movie or another movie about man's inhumanity to man. In this movie, I achieved a goal which he didn't really achieve. The last scenes are life-affirming. I cry sometimes when I see my own movie . . . you have at the end of the movie a scene that represents something that happened before the drama - a great moment that can never be reproduced again. In that sense, it's life-affirming."

· Irréversible premieres at the Edinburgh film festival on August 15 (tickets: 0131-623 8030), and will be released next year.